Communication within a power inverter using transformer voltage frequency

ABSTRACT

A power inverter may include a transformer serving as an isolation barrier. The power inverter may include a first controller on one side of the isolation barrier. The first controller may encode the frequency of an input voltage of the transformer with one or more operating conditions of a direct current power supply electrically coupled to the inverter. As second controller on the other side of the isolation barrier may determine a frequency associated with an output voltage of the transformer. The second controller may decode the frequency associated with the output voltage of the transformer to determine the encoded operating conditions.

BACKGROUND

1. Technical Field

The present embodiments relate to communicating by a power inverter.

2. Related Art

Power inverters may be used in various applications to provide alternating current (AC) power to a load using a direct current (DC) power source. In some applications, knowledge of the operating conditions of the DC power source may be desired to control the output. When electrical coupling is permitted, these operating conditions may be communicated to any point in the power inverter through standard wired communication manners. However, in particular applications, due to regulatory and/or safety requirements, a physical isolation barrier may be required. Existence of the isolation barrier may prevent communication of the operating conditions by electrical coupling.

SUMMARY

According to one aspect of the disclosure, a power inverter having a transformer may communicate information regarding operating conditions of DC power source through a voltage frequency of the transformer. The power inverter may include in input bridge to receive direct current (DC) power from the DC power source. The input bridge may convert a DC voltage from the DC power source to an AC voltage. The AC voltage may be applied to a first winding the transformer. The frequency of the AC voltage may be selected by a first controller based on the operating conditions of the DC power source. A second AC voltage may be generated across a second winding in the transformer due to application of the AC voltage applied to the first winding. A second controller may determine the frequency of the second AC voltage. The second controller may determine the operating conditions of the DC power source based on the frequency of the second AC voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.

FIG. 1 is a circuit diagram of an example power inverter having an isolation barrier.

FIG. 2 is a block diagram of an example controller of the power inverter of FIG. 1.

FIG. 3 is a block diagram of another example controller of the power inverter of FIG. 1.

FIG. 4 is a circuit diagram an example portion of the power inverter of FIG. 1.

FIG. 5 is a circuit diagram another example portion of the power inverter of FIG. 1.

FIG. 6 is a circuit diagram another example portion of the power inverter of FIG. 1.

FIG. 7 is one example of an operational flow diagram of the power inverter of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a circuit diagram of a power inverter 100. In one example, the power inverter 100 may convert direct-current power (DC) to alternating-current (AC) power. The power inverter 100 may receive power from a DC power source 102. In one example, the DC power source 102 may be photovoltaic-based, such as one or more photovoltaic (PV) modules. In FIG. 1, the power source 102 may be represented by a voltage source 104 coupled in series with a resistive element (R_(s)) 106. The inverter 100 may convert the DC power from the power supply 102 to AC power delivered at an AC output load 108 of the inverter 100. In alternative examples, other DC power sources may be implemented with the inverter 100.

The inverter 100 may include an input bridge (IB) 110. The input bridge 110 may include one or more circuit elements coupled to one another to convert the DC power from the DC power supply 102 to AC power. One example of the input bridge 110 is shown in FIG. 4. In FIG. 1, a line inductance (L_(l)) 112 coupled between the power supply 102 and the input bridge 110 is represented by an inductive element. The line inductance 112 may be one or more inductors used to reduce the current ripple transmitted to the DC power supply 102. The input bridge 110 may be coupled to a transformer 114 having a primary side 115 and secondary side 117. The primary side 115 of the transformer may include a first winding 116 and the secondary side 117 may include a second winding 118. Each of the first winding 116 and the second winding 118 may include more than one winding coupled in series or other configuration. The transformer 114 may have a winding ratio of 1:N to step up or step down the voltage and current from the output of the input bridge 110. A rectifier (RECT) 119 may be coupled to the second winding 118 of the transformer 114.

The AC power from the transformer 114 may be received by the rectifier 119. The rectifier 119 may include one or more circuit elements coupled to one another to convert the AC power from the transformer 114 to DC power. One example of the rectifier 119 is shown in FIG. 5. The rectified power, voltage and current, may be filtered by a filter capacitance (C_(f)) 120 represented in FIG. 1 as a capacitive element that is coupled in parallel to the rectifier 119. The filtered voltage and at least a portion of the current (see FIG. 4) from the rectifier 119 may be received by an output bridge 122. The output bridge 122 may include one or more circuit elements coupled to one another to convert the filtered DC power to AC power that may be delivered to an AC output load 108. One example of the output bridge 122 is shown in FIG. 5.

In FIG. 1, the inverter 100 may include a line filter 123 to filter output voltage of the output bridge 122 prior to the AC power being delivered to the output load 108. One example of the line filter 123 is shown in FIG. 6. In FIG. 1, the output load 108 may be a residential AC load having a split-phase configuration such as that found at residential premises in a United States electrical grid. In other examples, the output load 108 may be an industrial premises or any other load configured to receive AC power.

The output load 108 may be represented as a first voltage source (v_(l1)) 107 and a second voltage source (v_(l2)) 109 having an earth ground coupled between the two voltage sources 107 and 109. The output load 108 may also be represented as including a first line inductance (L_(OL1)) 111 and a second line inductance (L_(OL2)) 113 coupled between a respective voltage source 107 and 109 and the output bridge 122. An output sense resistor (R_(so)) 125 may be coupled between the output bridge 122 and the line filter 123. Current flowing through the output sense resistor 125 may be used to determine the current being provided to the output load 108.

Inverters such as the inverter 100 may implement an isolation barrier. An isolation barrier may provide at least one point of complete physical disconnection between components of the inverter 100. Use of the transformer 114 allows the inverter 100 to function with the existence of an isolation barrier. A physical gap exists between the first winding 116 and the second winding 118 with power being transferred through varying the mutual magnetic flux shared by the first winding 116 and the second winding 118 in order to induce a voltage across the second winding 118. No physical connection is used in providing electrical energy from the primary side 115 to the secondary side 117, thus, providing an isolation barrier. Use of an isolation barrier may be required in some circumstances due to regulatory requirements or safety concerns.

Use of an isolation barrier prevents the inverter 100 from having a common earth ground shared by all components of the inverter 100. Instead, portions of the inverter 100 may have separate groundings that may or may not be connected to an earth ground. Separate groundings allow a respective portion of the inverter 100 to be locally grounded, but may not be at the same potential as other portions. For example, in FIG. 1, the inverter 100 may be grounded separately on both the primary side 115 and the secondary side 117 of the transformer 114. The inverter 100 may be grounded on the DC side of the input bridge 110, as indicated by ground connection 126 in FIG. 1. The inverter 100 may also be grounded on the secondary side of the transformer 114. In particular, the inverter 100 may also be grounded on the DC side of the output bridge 122, or alternatively on the AC side of the output bridge 122, as shown by ground connections 128 and 130, respectively. In alternative examples, the groundings may be connected to other locations on the inverter 100 on the primary side 115 and/or the secondary side 117 of the inverter 100.

During operation of the inverter 100, knowledge of the operating conditions of the power supply 102 may be desired, such as the instantaneous voltage V_(DC) and current I_(DC). While these conditions may be monitored on the primary side 115 of the transformer 114, due to the isolation barrier in the inverter 100, no common physical connections are present connecting both the primary side 115 and secondary side 117 for monitoring. However, knowledge of the operating conditions on the primary side 115 of the transformer 114 may be desired to be available on the secondary side 117 of the transformer 114 in order to control power being delivered to the output load 108 or for informational purposes.

In FIG. 1, the inverter 100 may include a primary side controller (PSC) 132 and a secondary side controller (SSC) 134. The primary side controller 132 may determine the operating conditions (e.g., current, voltage, impedance, capacitance, other characteristics, or combinations thereof) from the power supply 102, such as the voltage V_(DC), from a sensor 133. The sensor 133 may be a voltage divider circuit or other circuit configured to sense the voltage produced by the power source 102. An input sense resistor (R_(si)) 135 may be used to provide the current I_(DC), or a current representative of I_(DC) to the primary side controller 132. Based on the operating conditions, the primary side controller 132 may generate one or more control signals 136 to control the output of the input bridge 114, as explained in further detail in FIG. 2.

During operation, the input bridge 110 may be controlled to generate an output voltage v_(ib) having a series of pulses alternating in polarity supplied to the first winding 116 of the transformer 114. Supplying the output voltage v_(ib) to the first winding 116 may cause a primary voltage v_(pri) to be applied across the first winding 116. Current flowing from the input bridge 110 (see FIG. 4) into the first winding 116 may cause the first winding 116 to experience a change in magnetic flux resulting in a secondary voltage v_(sec) being created in the second winding 118 on the secondary side 117 of the transformer 114.

The control signals 136 generated by the primary side controller 132 may control the duty cycle d (pulse width) and/or the frequency f_(p) of the pulses of the output voltage v_(ib). During operation, the input bridge 110 may be controlled by the primary side controller 132 to produce a voltage including pulses at a desired frequency f_(p). Thus, the frequency of the primary side voltage v_(pri) may have a frequency of f_(p) resulting in the secondary side voltage v_(sec) having a frequency of f_(p) as well. During operation, the frequency f_(p) may be varied within a particular range without any significant adverse effects regarding the desired output of the inverter 100. Varying the frequency f_(p) may allow information regarding the operating conditions of the power supply 102 to be conveyed to the secondary side 117 of the transformer 114 without physical connection to the primary side 115 of the transformer 114 or without the need to implement other manners of communication between the primary side 115 and the secondary side 117, such as wireless communication (e.g., light emitting diodes, radio frequency transmission, capacitive coupling, etc.) between the primary side controller 132 and the secondary side controller 134.

As the input bridge 110 generates pulses applied to the first winding 116 to generate the voltage v_(ib), the secondary side controller 134 may detect the secondary voltage v_(sec) across the second winding 118 through one or more sensors 140, such as voltage divider circuit, for example. The secondary voltage v_(sec) may be received by a rectifier 142. The secondary voltage v_(sec) may be buffered and scaled by a scaling device 143, such as an op amp, comparator, or other suitable device, in order to be compatible with logic-level integrated circuits. The output voltage v_(ro) of the rectifier 142 may be a unipolar pulse train with a frequency double that of the voltage v_(sec)−frequency f_(p). The secondary side controller 134 may determine the operating conditions of the power supply 102 based on the output voltage v_(ro) as further described with regard to FIG. 3. A communication device 146 may be used to transmit the operating conditions wirelessly, such as to a central authority for processing and analysis. In other examples, operating conditions of the DC power supply may be communicated through power lines electrically coupled to the output load 108 as an alternative to the communication device 146 or used in tandem.

FIG. 2 is a block diagram of an example of the primary side controller 132. In one example, the primary side controller 132 may be a microcontroller including a processor 200, a memory 202, clock 203, and I/O ports. The memory 202 may include one or more memories and may be non-transitory computer-readable storage media or memories, such as a cache, buffer, RAM, removable media, hard drive or other computer readable storage media. Computer readable storage media may include various types of volatile and nonvolatile storage media. Various processing techniques may be implemented by the processor 200 such as multiprocessing, multitasking, parallel processing and the like, for example. The processor 200 may include one or more processors.

The processor 200 may include an analog-to-digital converter (ADC) 204. Alternatively, the ADC 204 may be separate from the processor 200. The ADC 204 may receive the voltage V*_(DC) and current I*_(DC) of the power supply 102, which may be a voltage and current representative of the voltage V_(DC) and the current I_(DC), respectively, or the actual voltage V_(DC) and the current I_(DC). The ADC 204 may digitize these signals into one or more data signals 206 and provide the data signals 206 to a frequency determination module (FDM) 208. The modules are software, hardware or some combination thereof executable by a processor, such as the processor 200. Software modules may include instructions stored in the memory 202, or other memory device, that are executable by a processor or processors. Hardware modules may include various devices, components, circuits, gates, circuit boards, and the like that are executable, directed, and/or controlled for performance by a processor. The FDM 208 may determine the frequency f_(p) of the input bridge 110 output based on the current operating conditions of the power supply 102.

During operation, the FDM 208 may receive the data signals 206 from the ADC 204 indicative of the power supply voltage V_(DC) and current I_(DC). The FDM 208 may include a read module (RM) 210. The read module 210 may receive the data signals 206 from the ADC 204 to determine the voltage V_(DC) and current I_(DC) based on the data signals 206 and, in one example, the read module 210 may determine if the data signals 206 are valid. The FDM 208 may also include an update module (UM) 212. The update module 212 may receive a clock signal from the clock 203 used to generate a periodic update signal (UP D) 219. The periodic update signal 219 may indicate to the read module 210 the time at which the read module 210 may sample the data signals 206. The periodic update signal 219 may be generated at a predetermined update period of T_(update). In other examples, the update period T_(update) may be dynamically adjusted during operation of the inverter 100.

Upon receipt and completion of any validation techniques, the read module 210 may provide the data 206 to an encoding module (EM) 214. In the example of FIG. 2, the encoding module 214 may retrieve encoding data 216 from the memory 202. The encoding data 216 may indicate a particular frequency at which to control the frequency f_(p) of output voltage V_(ib) in order to convey the operating conditions of the power supply 102 to the secondary side 117 of the transformer 114. In one example, the encoding data 216 may include one or more tables mapping particular frequency values to particular operating condition points of the power supply 15 102. Table 1 below is one example of the encoding data 216 in which the desired operating frequency range of the input bridge 110 has a midpoint of approximately 50 kHz.

TABLE 1 Current/ Voltage 0 A 0.5 A 1.0 A 1.5 A . . . 10 A   0 V 49,500 Hz 49,550.5 Hz 49,551 Hz 49,551.5 Hz . . . 49,509.5 Hz 0.5 V 49,510 Hz 49,510.5 Hz 49,511 Hz 49,511.5 Hz . . . 49,519.5 Hz 1.0 V 49,520 Hz 49,520.5 Hz 49,521 Hz 49,521.5 Hz . . . 49,529.5 Hz . . . . . . . . . . . . . . . . . . . . . 50.0 V   50,490 Hz 50,490.5 Hz 50,491 Hz 50,491.5 Hz . . . 50,499.5 Hz

In one example, the desired operating condition to convey to the secondary side 117 may be the voltage V_(DC) and current I_(DC) provided by the power supply 102. Table 1 includes a frequency corresponding to a voltage and current for the voltage V_(DC) and the current I_(DC), in increments of 0.5 V and 0.5 A, from a range of 0V to 50V and 0 A to 10 A. The output voltage v_(ib) of the input bridge 110 may be controlled at one of the particular frequencies listed in Table 1 to convey a corresponding operating condition point. In alternative examples, the encoding data 216 may include other data allowing selection of the frequency f_(p), such as equation-based data, frequency shift keying, or orthogonal frequency division multiplexing.

In using tables, such as Table 1, the encoding module 214 may round the instantaneous values of the current I_(DC) and voltage V_(DC) in order to select the corresponding frequency. Upon selection of the frequency by the FDM 208, the frequency f_(p) may be provided to a pulse width modulator (PWM) 218. The PWM 218 may also receive the data 206 to determine the duty cycle d independently from the FDM 208. The PWM 218 may generate the control signals 136 based on the data 206 and frequency f_(p) provided by the FDM 208.

FIG. 3 is a block diagram of an example of the secondary side controller 134. The secondary side controller 134 may be a microcontroller that includes a processor 300, memory 302, as well as I/O ports, and clock (CLK) 304. The processor 300 may include an ADC 306. Alternatively, the ADC 306 may be separate from the processor 300. The ADC 306 may receive and digitize the voltage Vro and provide a data signal 308 indicative of the voltage Vro to a condition determination module (CDM) 310 executed by the processor 300 or other hardware. The CDM 310 may determine the operating conditions conveyed through the frequency fp based on the data signal 308. The CDM 310 may include a pulse counter module (PCM) 312. The PCM 312 may determine the number of pulses included in the voltage Vro signal over a predetermined read period T_(read).

The number of pulses 314 may be relayed from the PCM 312 to a decoding module 10 (DM) 316. The decoding module 316 may determine the operating conditions corresponding to the number of pulses counted over by the PCM 312 over the period T_(read). In one example, the decoding module 316 may implement decoding data 318 stored on the memory 302. The decoding data 318 may include various operating points of the operating conditions of the power supply 102 that correspond to the number of pulses read over the period T_(read). In one example, the decoding data 318 may include one or more tables having operating conditions of the power supply 102. In one example, a desired output frequency range of the input bridge 110 may have a midpoint of approximately 50 kHz. The frequency f_(p) may be modulated within a range of about +/−5% of a particular switching frequency, however, in order to convey operating condition information regarding the power supply 102 to the secondary side 117 of the transformer 114. Other tolerances are possible. The decoding data 318 may include tables having a number of possible operating conditions points of the power supply 102. Each possible operating condition points in the table may correspond to a particular number of pulses counted by the pulse counter over the period of T_(read).

The number of pulses 314 may be relayed from the PCM 312 to a decoding module (DM) 316. The decoding module 316 may determine the operating conditions corresponding to the number of pulses counted over by the PCM 312 over the period T_(read). In one example, the decoding module 316 may implement decoding data 318 stored on the memory 302. The decoding data 318 may include various operating points of the operating conditions of the power supply 102 that correspond to the number of pulses read over the period T_(read). In one example, the decoding data 318 may include one or more tables having operating conditions of the power supply 102. In one example, a desired output frequency range of the input bridge 110 may have a midpoint of approximately 50 kHz. The frequency f_(p) may be modulated within a range of about +/−5% of a particular switching frequency, however, in order to convey operating condition information regarding the power supply 102 to the secondary side 117 of the transformer 114. Other tolerances are possible. The decoding data 318 may include tables having a number of possible operating conditions points of the power supply 102. Each possible operating condition points in the table may correspond to a particular number of pulses counted by the pulse counter over the period of T_(read).

Table 2 includes an example of a table that may be included in the decoding data 318.

TABLE 2 Voltage/Current 0 A 0.5 A 1.0 A 1.5 A . . . 10 A   0 V 99000 99001 99002 99003 . . . 99019 0.5 V 99020 99021 99022 99023 . . . 99039 1.0 V 99040 99041 99042 99043 . . . 99059 . . . . . . . . . . . . . . . . . . . . . 50.0 V  100980  100981 100982  100983  . . . 100999  Table 2 may be applied to the situation in which the voltage produced of the power supply 102 is to be conveyed to the nearest 0.5 V and the current produced by the power supply 102 is to be conveyed to the nearest 0.5 A. In Table 2, approximately 50 kHz may be the midpoint of the frequency range in which the output of the input bridge 114 is desired to operate resulting in 100 discrete voltage values and 20 discrete current values that may occur according to Table 2. Thus, there are a total of 2,000 possible combinations of voltage and current. As such, 2,000 possible pulse counts are used within the given time frame. When the frequency f_(p) is at 50 kHz, the pulse counter module 148 may count 100,000 pulses. There would be a 2001 pulse difference between 99 kHz, (99,000 pulses per second) and 101 kHz (101,000 pulses per second). Based upon Table 2, the secondary side controller 134 determines the voltage and current of the power supply 102 based on the counted number of pulses over the read period T_(read). In Table 2, the read period T_(read) is one second.

A read/update module (R/U) 320 may provide a read signal (RD) 322 and an update signal (UD) 324 to both the pulse count module 312 and the decoding module 316. The read/update module 320 may receive a clock signal from the clock 304 used to generate the read signal 322 and update signal 324. The read signal 322 may indicate to the PCM 312 the time at which to start counting the pulses in the data signal 308. Upon receiving the update signal 324, the PCM 312 may restart the counting. The read signal 322 and the update signal 324 may be coordinated such that read signal 322 is sent after the update signal 324. The read signal 322 may also indicate a duration of time over which to count the pulses or an end time. In one example, T_(update) may be much greater than T_(read). For example, T_(read) may be one second in duration, while T_(update) may be several minutes. In such an example, the pulse counter module 312 may count the number of pulses over several periods of T_(read) and take the average number of pulses per read period T_(read). This average value may be used to by the encoding module 316 to identify the operating condition of the power supply.

The secondary side controller 134 may also detect the frequency of the secondary voltage v_(sec) without use of the rectifier 142. In one example, the scaling device 143 may be an available device within the secondary side controller 134. The scaling device 143 may scale the secondary voltage v_(sec) and the secondary side controller 134 may detect the frequency directly from the scaled version of the secondary voltage v_(sec). The encoding data 318 may include data representative of that shown in Table 1.

FIG. 4 is a circuit diagram of an example of the power supply 102, and input bridge 110, transformer 114, and rectifier 119 of the inverter 100. In FIG. 4, the power supply 102 of FIG. 2 may be a photovoltaic module 400 including one or more photovoltaic cells. In FIG. 4, the PV module 400 is grounded and may generate a voltage Voc based on the received solar energy. A filter capacitor C_(pu) is coupled in parallel to the PV module 400. The current I_(DC) may be supplied from the PV module 400.

The input bridge 110 may include a plurality of switches 404. Each switch 404 in FIG. 4 is individually designated as SWI-4. In the example of FIG. 4, each switch 404 is embodied as a metal oxide semiconductor field-effect transistor (MOSFET). The term MOSFET may refer to other field effect transistors, such as those having a gate material other than metal, such as polysilicon (polycrystalline silicon) or other suitable gate material. The term MOSFET may also include insulated gate bipolar transistors (IGBTs) and insulated-gate field-effect transistors (IGFETs) as well. Other suitable switch types may be used for SW1 through SW4. In FIG. 4, each switch 404 may include an intrinsic body diode 406, individually designated as BD 1-4. Each switch 404 may include a gate (G), drain (D), and source (S). The switches 404 may be coupled to one another in order to convert the DC power generated by the power supply 102 to AC power. The input bridge 110 may supply the AC power to the first winding 116 of the transformer 114. The input bridge 110 may be controlled by the primary side controller 132 (not shown) through the control signals in order to provide the current to the first winding 116 alternating the polarity of the supplied current in order to generate a voltage across the second winding 118.

The primary side controller 132 may generate the controls signals 136 to operate the switches 404 in such a manner. The control signals 136 generated by the primary side controller 132 may include a pair of control signals C1 and C2. The first winding 116 may be coupled to the input bridge 114 such that when control signal C1 is applied to the gates of switches SW1 and SW4 and the control signal C2 is not applied to the switches SW2 and SW3, the current IDe may flow through the switches SW1 and SW4. Current flowing through the switches SW1 and SW 4 may be considered positive in polarity with respect to the first winding 116. When negative current with respect to the first winding 116 is desired, the control signal C2 may be applied to the switches SW2 and SW3 and the control signal C1 is not applied to the switches SW1 and SW2, the current may flow through the switch SW2, through the first winding 116, and through the switch SW3. The frequency with which the switching signals C1 and C2 are alternately applied to the switches 204 represents the frequency with which the output pulses of the input bridge 114 are applied to the first winding 116—frequency fp. The length of time the switch pairs SW1-4 and SW2-3 remain on determines the width (duty cycle d) of a particular pulse.

Upon generation of the pulses of the input bridge 114 to the first winding, the secondary voltage Vsec may be generated across the second winding 118. The rectifier 119 may include a plurality of diodes 210, individually designated as D1-D4 in FIG. 4, coupled to one another to convert the AC power received from the secondary side 117 of the transformer 114 to DC power. In FIG. 4, the second winding current i_(sec) may be considered positive with respect to the second winding 118 in the direction indicated in FIG. 4. Positive current i_(sec) flowing through the second winding 118 will also flow through diodes D2 and D3, causing the rectifier output current i_(r) to be positive with respect to the output load 108 (not shown). When the current i_(sec) induced in the second winding 118 is negative, the current i_(sec) will flow through the diodes D1 and D4, causing the current if to be positive with respect to the output load. Thus, the current flowing out of the rectifier 119, current i_(sec) will be DC current. A portion of the current i_(r), designated as i_(cf), will flow the filter capacitor C_(f), the difference of current i_(b) will flow towards the output bridge 108.

FIG. 5 is circuit diagram of an example of the output bridge 122. The output bridge 122 may include a plurality of switches 500, individually designated as SW5-S, coupled to one another to convert the DC power received from the rectifier 119 to AC power. The switches 500 may be similar to the switches 404 in FIG. 4. For example, the switches 500 may be MOSFET switches each having an intrinsic body diode 502, individually designated as BD5-8. The switches 500 may receive control signals CS3 and CS4 from the secondary side controller 134 (not shown) or other suitable controller. Operating in manner similar to the input bridges 114, when switches SW5 and SWS receive control signals CS3 and switches SW6 and SW7 do not receive control signal CS4, the current i_(b) will flow through switches SW5 and SWS causing the output current i_(oc) of the output bridge 122 to be positive with respect to the output load 108. When the control signals C3 and C4 are alternated, e.g., switches SW2 and SW3 turned on and SW1 and SW4 turned off, the current i_(oc) and voltage v_(oc) may be negative in polarity with respect to the output load 108.

FIG. 6 is a circuit schematic of an example of the line filter 123 connected to the output load 108. The line filter 123 may include filter inductances (L_(lf1)) 600 and (L_(lf2)) 602 each individually represented as a single inductor. However, the filter inductances 600 and 602 may each include single or multiple inductors. A filter capacitance (C_(lf)) 604 may be electrically coupled between the filter inductances 600 and 602 and connected in parallel with the output load 108.

During operation, the current i_(oc), when positive with respect to the output load, may flow through the filter inductance L_(l1) in the direction indicated in FIG. 6. A portion of the current i_(oc) may flow through the filter capacitor 604, represented as current i_(lf). The difference in current, current i_(load), may flow through the output load 108. The line filter 123 acts to smooth the output current i_(oc) flowing from the output bridge 122. As the inverter 100 continues to operate, the polarity of the current i_(oc) alternates flowing through the output load 108 in an opposite direction as that described.

FIG. 7 is an operational flow diagram of example communication of information associated with the power supply 102 by the inverter 100. In one example, the primary side controller 132 and the second side controller 134 may be initialized (block 700) such as an initial start-up or system reboot scenario. Upon initialization, the read period T_(read) and the update period T_(update) may be set (block 702). The primary side controller 132 may determine the operating conditions of the power supply 102 (block 704), such as the voltage and/or current, for example. The primary side controller 132 may determine a corresponding frequency and/or PWM of the operating conditions (block 706), such as through look-up tables, predetermined equations, or other manner.

The primary side controller 132 may control the input bridge 110 to output a voltage having the determined frequency and/or PWM (block 708). The voltage of the input bridge 110 may be applied to the primary winding 116 of the transformer 114 generating the secondary voltage v_(sec) across the secondary winding 118. The secondary side controller 134 may determine the frequency and/or PWM of the secondary voltage v_(sec) over the read period T_(read) (block 710). The secondary side controller 134 may determine the operating conditions of the DC power source 102 based on the frequency and/or PWM of the secondary voltage v_(sec) (block 712). The primary side controller 132 may determine if the update period T_(update) (block 714) has expired. Upon expiration of the update period T_(update), the primary side controller 132 may determine the current operating conditions of the DC power supply. If the update period T_(update) has not expired, the primary side controller 134 may continue to determine the frequency and/or PWM of the secondary voltage v_(sec) during the read period T_(read).

While FIGS. 1-7 illustrate and describe communication using the transformer 114 through the inverter 100, such communication may be extended to various power converter and inverter topologies. For example, communication via the transformer 114 may be applied to various power converters used to convert AC power to DC power, such as buck, boost, and flyback converters, for example. While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. The various embodiments described herein include a variety of electrical elements and combinations of electrical elements, such as inductors, capacitors, voltage sources, switches, resistors, diodes, and power converters electrically coupled in various manners. The described example configurations of electrical elements and devices are examples that may be embodied through equivalent configurations having additional or fewer of the described elements, circuits, and devices, and alternative elements, alternative circuits, and/or alternative devices while remaining within the scope of invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. 

I claim:
 1. A power inverter comprising: a bridge circuit configured to convert an output voltage of a direct-current (DC) power source to an alternating-current (AC) output voltage having an output frequency; a transformer having a primary side winding and a secondary side winding magnetically coupled to one another, wherein the primary side winding is configured to receive the AC output voltage; and a first controller having a processor and a memory, wherein the processor is configured to: determine at least one operating condition of the DC power source using a voltage or a current sensed at the DC power source; and control the output frequency of the AC output voltage in response to the at least one operating condition, wherein the first controller includes an encoding module to select the output frequency based on the sensed voltage or the sensed current and, wherein the encoding module rounds a value for the sensed voltage or the sensed current to select the output frequency.
 2. The power inverter of claim 1, wherein the memory of the first controller is configured to store a plurality of predetermined operating conditions and a plurality of predetermined frequencies, wherein each of the plurality of predetermined operating conditions corresponds to a respective one of the plurality of predetermined frequencies, wherein the processor of the first controller is configured to: select one of the predetermined operating conditions from a first table based on the at least one operating condition; and control the output frequency of the AC output voltage to a predetermined frequency corresponding to the selected one of the operating conditions.
 3. The power inverter of claim 1, comprising a second controller having a processor and a memory, the processor configured to: determine a frequency of a voltage of the secondary winding; and determine the at least one operating condition based on the frequency of the voltage of the secondary winding.
 4. The power inverter of claim 3, wherein the memory of the first controller is configured to store a plurality of predetermined frequencies and a plurality of predetermined operating conditions of the DC power supply, wherein each of the plurality of predetermined frequencies corresponds to a respective one of the plurality of predetermined operating conditions, wherein the processor of the second controller is configured to: select one of the plurality of predetermined frequencies that corresponds to the determined frequency of the voltage of the secondary winding; and select the predetermined operating condition of the DC power supply that corresponds to the selected one of the plurality of predetermined frequencies.
 5. The power inverter of claim 3, wherein power inverter further comprises: a rectifier configured to rectify the voltage of the secondary winding; an inverter configured to invert the rectified voltage; determine a frequency of the inverted voltage; and determine the at least one operating condition based on the frequency of the inverted voltage.
 6. The power inverter of claim 3 further comprising an output bridge circuit having an AC output voltage, wherein the output bridge circuit is configured to supply an AC output voltage to an AC load, wherein the second controller is configured to control a frequency of the AC output voltage of the output bridge circuit based on the at least one operating condition.
 7. The power inverter of claim 1, wherein the at least one operating condition is at least one of the output voltage of the DC power source and an output current of the DC power source.
 8. The power inverter of claim 1, wherein the first controller and a second controller are electrically isolated from one another.
 9. The power inverter of claim 1, wherein the processor is configured to vary the output frequency to convey information regarding the at least one operating condition without a connection to the secondary side.
 10. The power inverter of claim 1, further comprising a communication device to transmit the at least one operating condition.
 11. The power inverter of claim 10, wherein the communication device transmits over a wireless network.
 12. The power inverter of claim 1, wherein the controller is configured to generate a periodic update signal that indicates when to sample data signals corresponding to the voltage or the current.
 13. The power inverter of claim 1, wherein the controller is configured to control the output frequency using encoding data comprising equation-based data, frequency shift keying data or orthogonal frequency division multiplexing data.
 14. The power inverter of claim 1, wherein the controller includes a pulse width modulator to receive the output frequency and to determine a duty cycle.
 15. A power inverter comprising: a bridge circuit configured to convert an output voltage of a direct-current (DC) power source to an alternating-current (AC) output voltage having an output frequency; a transformer having a primary side winding and a secondary side winding magnetically coupled to one another, wherein the primary side winding is configured to receive the AC output voltage; a first controller having a processor and a memory, wherein the processor is configured to: determine at least one operating condition of the DC power source using a voltage or a current sensed at the DC power source; and control the output frequency of the AC output voltage in response to the at least one operating condition; and a secondary side controller, wherein the secondary side controller is configured to determine a number of pulse counts over a read period for the output frequency.
 16. The power inverter of claim 15, wherein the number of pulse counts is between 1900 and 2100 counts.
 17. The power inverter of claim 15, wherein the read period is about 1 second.
 18. The power inverter of claim 15, wherein a read signal indicates when to start the pulse count.
 19. The power inverter of claim 18, wherein an update signal restarts the pulse count.
 20. The power inverter of claim 19, wherein an update period corresponding to the update signal is greater than the read period.
 21. The power inverter of claim 20, wherein the secondary side controller is configured to determine whether the update period has expired.
 22. The power inverter of claim 15, wherein the secondary side controller is configured to determine an average number of pulses over a plurality of read periods.
 23. The power inverter of claim 22, wherein the secondary side controller is configured to use the average number of pulses to identify the at least one operating condition. 